Service desk - each mail response create new ticket

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Problem to solve

Describe your question in as much detail as possible:

Service desk is well configured and everything is fine, except when someone reply to the mail, instead of completing the opened ticket, it creates an another one, each time someone reply

Steps to reproduce

Sending mail to our support address, which transfers ce mail to the mail gitlab listen to.
when someone reply to the original email → recreates a new ticket instead of appending to the original one

Configuration

Versions

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Versions

It would suggest that reply by email hasn’t been configured: Reply by email | GitLab and: Incoming email | GitLab